1. Field of the Invention
The present invention relates to a method for controlling the peak cell rate spacing of multiplexed ATM traffic, and more particularly to a method for controlling the peak cell rate for multiple virtual channel connections which can secure a peak cell rate negotiated between a user and a network.
2. Description of the Prior Art
In asynchronous transfer mode (ATM) networks, network resources are allocated through a negotiation between a user and a network during the connection establishment phase. To prevent the ATM network from reaching an unacceptable congestion level due to an intentional excess of the negotiated parameters, it is necessary to monitor whether or not the traffic flow on every virtual channel connection (VCC) conforms to the negotiated traffic parameters. This is called a policing or a usage parameter control (UPC) function. At present only the peak cell rate, among traffic parameters, is defined in Recommendation I.371 by the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T).
However, the peak cell rate monitored during the usage parameter control is usually different from the peak cell rate generated at the source (negotiated between the user and the network). This is due to the cell delay variation, which changes the cell flow generated in the source of the ATM connection. The cell delay variation is principally caused by the competing demands of cells to share the same resources, the same queue, or the same trunk. Therefore, with the monitoring function which monitors the peak cell rate not considering the cell delay variation, a mistaken judgment of violating traffic could occur even when a user complies with the negotiated peak rate.
Accordingly, cell delay variation tolerance should be included in the monitoring function, but this would make it more difficult to monitor users who intentionally send traffic beyond the negotiated amount. In addition, the efficiency of the bandwidth could drop considerably if a wide cell delay variation tolerance were set up.
Previous technologies to solve these problems are the space controller and the spacing policer. The spacing policer calculates a time D when a cell of a connection, which arrived at the spacing policer at a time T, is to leave, and links the cell to a (T+D) location. Here, D indicates the number of cell time slots for securing a minimum transfer interval between cells of the connection. However, if multiple cells are linked to the (T+D) location, only one cell is output at the (T+D) location and the rest are delayed. This phenomenon is called "output contention." If the next arriving cells are output without delay, the peak interval of the connection could become smaller than desired. According to the result of a simulation, it has been shown that approximately 20% of the cells can be transferred faster than the desired peak interval. The spacer controller compares the theoretical cell arriving time and the present arriving time "t" using variables indicating a theoretical cell arriving time (TAT). If "t" is smaller than TAT, it saves the cells at the TAT location in a retransfer memory so as to let the cells arriving at the present time leave at the TAT time, and secures a desired peak interval between cells. However, even with this method, an interval smaller than the negotiated peak interval may occur due to output contention.
Therefore, the conclusion can be made that transfers with the interval smaller than the negotiated peak interval complicate the bandwidth assignment strategy and drop the band efficiency.